MM-43084 update product limits through webhook and websocket (#20076)

* Define interfaces for updating subscriptions and product limits from CWS webhook.

app/plugin_api.go

@@ -1179,3 +1179,9 @@ func (api *PluginAPI) RequestTrialLicense(requesterID string, users int, termsAc
 
 	return api.app.Channels().RequestTrialLicense(requesterID, users, termsAccepted, receiveEmailsAccepted)
 }
+
+// GetCloudLimits returns any limits associated with the cloud instance
+func (api *PluginAPI) GetCloudLimits() (*model.ProductLimits, error) {
+	limits, err := api.app.Cloud().GetCloudLimits("")
+	return limits, err
+}